资料题：According to Dr.Joel Sapper, headaches result from（  ）。

Reading to oneself is a modem activity which was almost unknown to the scholars of the classical and medieval(中世纪的) worlds, while during the 15th century the tern"reading"undoubtedly meant reading aloud.Only during the 19th century did silent reading become commonplace .One should be wary, however, of assuming that silent reading came about simply because reading aloud is a distraction to others.Examination of factors related to the historical development of silent reading reveals that it became the usual mode of reading for most adult reading tasks mainly because the tasks themselves changed in character.The last century saw a steady gradual increase in literacy, and thus in the number of readers.As readers increased, so the number of potential listeners declined, and thus there was some reduction in the need to read aloud.As reading for the benefit of listeners grew less common, so came the flourishing of reading as a private activity in public places as libraries, railway carriages and offices, where reading aloud would cause distraction to other readers.Towards the end of the century there was still considerable argument over whether books should be used for information or treated respectfully, and over whether the reading of materialsuch a newspapers was in some way mentally weakening.Indeed this argument remains with us still in education.However, whatever its virtues, the old shared literacy culture had gone and was replaced by the printed mass media on the one hand and by books and periodicals for a specialized readership on the other.By the end of the century students were being recommended to adopt attitudes to books and to use skills in reading them, which were inappropriate, if not impossible, for the oral reader.The social, cultural, and technological changes in the century had greatly altered what the term"reading" implied.